In the 3rd Generation Partnership Project (3GPP) Long-Term Evolution (LTE) fourth generation mobile communication standard, base stations, so-called enhanced NodeBs or eNodeBs (eNBs), schedule the transmissions of common channels in the physical layer (PHY) via the cell-specific periodic wideband Physical Downlink Control Channel (PDCCH). In addition, the reference signals, with which user equipment (UE) can demodulate the PDCCH, are also transmitted in a cell-specific periodic wideband fashion.
Previous studies to enhance the LTE Advanced (LTE-A) communications standard have focused on lean reference signal design. For example, in LTE Release 11, a standalone New Carrier Type (NCT) for Primary Cells (PCells) was proposed but not adopted. In the subsequent Release 12, small cell enhancements were introduced which allow small cell eNBs to turn on and off their transceiver circuitry depending on the traffic load. However, these enhancements only apply to Secondary Cells (SCells), whereas UEs are not allowed to camp on such cells operating in small cell on/off mode. In fact, there is no lean carrier waveform in LTE-A. Instead, for LTE-A, overhead is controlled by switching between no transmission and transmission of legacy waveforms, i.e., those standardized since LTE Release 8.
For example, a PCell can slowly ramp down its transmit power to simulate the effect of mobility at the UE, thus triggering a handover to an adjacent cell. Once all the UEs are handed off from the respective PCell, the eNB can turn off its radio front-end, resulting in the desired energy savings and interference reductions, namely, spectral efficiency enhancements. Moreover, the eNB turning off the PCell can use the X2 Application Protocol (X2AP), used on the X2 interface connecting eNBs, to communicate to other eNBs the reason for turning off the PCell in question. This ensures that ping-pong effects are avoided, for example, the event in which an adjacent eNB tries to hand over a UE back to the PCell that is to be turned off. This allows eNBs to turn cells on and off, and subsequently, to turn their RF circuitry on and off. Nevertheless, when the PCell is active (namely, not in energy savings mode), a properly operating eNB transmits Release 8 wideband, periodic, cell-specific waveforms for backward compatibility reasons.
For SCells, LTE Release 12 provisions a more dynamic scheme which uses Release 10 Carrier Aggregation (CA) procedures to (de)activate SCells based on the short-term traffic load in the Medium Access Control (MAC) layer buffer of the eNB. For a deactivated SCell, the eNB only sends Discovery Reference Signals (DRS). Further, the eNB can control the transmission bandwidth and periodicity of the DRS using the Radio Resource Control (RRC) protocol. However, similar to the previous example, when the SCell is activated, proper eNB operation dictates that Release 8 wideband, periodic, cell-specific waveforms are transmitted for backward compatibility.
Thus, a method is desired in which system information can be obtained by the user equipment in a manner that overcomes the shortcomings of the prior art.